This invention relates generally to the area of internal combustion engine fuel injectors and more particularly to an electronically controlled, hydraulically actuated pressure amplification device for compression-ignition engine fuel injectors.
Those skilled in the art are aware that fuel injection systems are an essential element of design and application for compression-ignition engines which rely on the high temperature of a rapidly substantially adiabatically, compressed charge of air to provide spontaneous ignition of a charge of fuel introduced near the maximum compression point of the cycle. To complete as fully as possible the combustion process, it is necessary to develop a sufficiently high fuel injection pressure external to the cylinder to overcome the pressure within the engine cylinder, and to rapidly inject the fuel at the most advantageous time in the cycle. It is well known that a certain proportion of the fuel charge may be introduced early in the compression stroke to facilitate evaporation and assist the propagation of the flame front after ignition occurs. However, this so-called multi-phase injection is difficult to achieve with mechanically operated fuel injection systems.
The heretofore predominant method used for injecting fuel is the mechanical/hydraulic plunger driven by cam shaft means in fixed mechanical relationship to the angular position of the engine crankshaft. The plungers are alternatively located in injector cylinders adjacent to the engine combustion chambers or remotely located in a fuel injection pump separately mounted on the engine and driven through gear and shaft means.
Existing commercial automotive diesel engines traditionally have been equipped with fuel injection equipment based on the principles of the Bosch system. In the Bosch system, a mechanically driven cam shaft causes a plunger to reciprocate within a finely ground and lapped cylinder barrel and eject a predetermined amount of fuel oil under high pressure through several small exist holes of an injector nozzle into the engine combustion chamber beginning near the time of top dead center position of the crank throw. The fuel is broken up or "atomized" by the injection process and is sprayed as droplets, within the combustion chamber in a penetration pattern which is dependent upon the size of the injector holes and their orientation. The droplets are then vaporized and ignited by the air movement and temperature of the compressed charge. Combustion is completed by the swirl or motion of air flow patterns which are a function of the design of the cylinder head and valve gear, the piston cavity design, and other cylinder-to-cylinder variables as those skilled in the art are aware.
The design arrangement for the location of the fuel injectors varies according to the manufacturer. A jerk type injection pump may be located removely from the cylinder head and supply the fuel under high pressures through thick wall tubing to the injectors. Alternatively, the fuel injector cam shaft may be integrated with the air intake poppet valve camshaft and/or exhaust valve camshaft(s) to actuate the fuel injectors directly.
In the prior art, the fixed mechanical relationship and dependence of injector actuation and timing on the design of camshaft lobes and gear drive mechanisms requires the use of complex control features for precise control of variable speed/variable power engines. These control features adjust the supply of fuel for a single injection of fuel per cycle per cylinder for accommodation of variable load conditions at fixed engine speed, for acceleration of coupled masses to operating speeds, for control of overrun or overshoot, and for fuel-air enrichment needed under starting conditions. The fuel injector plunger barrels are sometimes rotatable by a rack and pinion mechanism and by mechanical flyball governing systems which vary the admission and fuel injection cutoff timing by means of controllable sleeve valve port opening arrangements. Adjustments for variation in fuel density or for operation at altitudes usually are also provided.
The mechanical design arrangements and control mechanisms heretofore known and in use today represent a compromise between the ideal of instant and precise response to load demand variation for each engine cylinder under all operating conditions on the one hand, and the practical consideration of injection equipment cost, serviceability and maintainability on the other. They do not commonly accommodate multi-phase injection. Wear of mechanical fuel injection equipment, including cams, roller followers, plungers and barrels, governor linkages, and control rods and bearings, all contribute to the frequent need for repair and maintenance by skilled personnel to avoid damage, loss of performance and excessive or deleterious emissions.
Among the patents which may be considered of interest only relative to this invention are U.S. Pat. Nos. 3,961,612; 3,257,078; 3,752,137; and 3,587,547.